Data communication networks may include various switches, routers, hubs, and other devices coupled to and configured to receive data and forward the data on the network. These devices will be referred to herein as “network elements.” A network element is generally not a consumer of the data, but rather is used to receive and forward data so that the data may pass through the network. Data is communicated through a network by enabling the network elements to pass protocol data units, such as frames, packets, cells or segments, between each other over communication links. A particular protocol data unit may be handled by multiple network elements and cross multiple communication links as it travels between its source and its destination over the network.
The various network elements on the communication network communicate with each other using predefined sets of rules, referred to herein as protocols. Different protocols are used to govern different aspects of the communication, such as how signals should be formed for transmission between the network elements, various aspects of what the protocol data units should look like, how protocol data units should be handled or routed through the network by the network elements, and how information such as routing information should be exchanged between the network elements.
A network service provider will generally implement one or more data centers to enable customers to connect to a communication network such as the Internet. Likewise, in an enterprise, a data center may be used to house servers that enable users to connect to the corporate network or which provide other services on the network. Example services include database services, email services, etc.
In a data center, a large number of servers (e.g. 24 servers) may be housed in a rack and connected to an Ethernet Switch Unit which connects the servers to a communication network. Typically, the Ethernet Switch Unit will be co-located with the rack of servers. The Ethernet switch unit will then connect to a large Gateway switch which will connect the Ethernet switch unit to higher bandwidth network such as a routed Ethernet network.
FIG. 1 shows an example data center in which servers 10 connect to one or more Ethernet switch units 12, which in turn are connected to gateways 14. The gateways 14 provide connectivity to a routed Ethernet network 16. The Ethernet switch units will generally be dual-homed to a pair of gateway switches so that, if one of the gateway switches should fail, the other gateway can assume responsibility for forwarding traffic into the routed Ethernet network. For example, in FIG. 1, each of the Ethernet switch units 12 are connected to two different gateways (e.g. dual homed) to a pair of gateway switches 14. The gateway switches may individually assume responsibility to represent particular ESUs into the routed Ethernet network or, alternatively, may collaboratively represent the ESUs into the routed Ethernet network by treating the links from the ESUs to the gateways as a split multi-link trunk.
Although it is possible to envision multiple ESUs in a chain connected to a pair of gateway nodes, such a configuration is vulnerable to multiple failures. Hence dual homing of individual switches directly to the gateways is desirable since the configuration is less susceptible to failure.
Large data centers may require layer two connectivity for communities of 10s to 100s of thousands of servers. To enable this configuration to be able to scale, one of the key metrics to consider is the number of MAC addresses the gateway is required to advertise into the routed Ethernet network to represent the set of subtending servers. Specifically, when the ESU is connected directly to the gateway, the gateway will need to advertise the MAC address of the port via which the ESU is reached into the routed Ethernet network Normally as the number of Ethernet switch units increases, the associated number of ports, and hence the number of MAC addresses being advertised into the routed Ethernet network (e.g. an Ethernet network implemented using 802.1aq Shortest Path Backbone Bridging, although this may also apply to 802.1ah spanning tree controlled Ethernet networks) may become excessive and expensive for the core to maintain. Accordingly, it would be advantageous to provide a way to reduce the number of MAC addresses that is required to be advertised into the routed Ethernet network.